Oysters tell us why the Earth descended into a Little Ice Age hundreds of years ago

Some scientists are turning to “whispers” to better predict when our planet’s climate will turn into dangerous regions.

The narrow-lipped oyster may seem like a strange creature for researchers to turn their ears to, but as we get closer to learning, clams are exceptional natural historians.

Similar to tree rings, the growth bands on their shells contain important information about the environment and how it has changed over the years.

Like memoir lines, these complex passages can be separated and read by scholars centuries after they were first “written”.

In fact, the ancestors of oysters have been laying corridors in the mineral calcite for more than five hundred million years, nearly three hundred million years before the emergence of the dinosaurs, giving us an unprecedented window into past climates.

Now, these ancient archives are issuing a stark warning. A new reading of three bivalve records from the northern Icelandic shelf has revealed a potentially dangerous tipping point in Earth’s climate.

The results suggest that the shift in our global climate about eight centuries ago was the result of a feedback loop that eroded the stability of the North Atlantic climate system, pushing it into a new, colder-than-normal state.

The “Little Ice Age” first began in the 13th century in the North Atlantic and only stopped when anthropogenic heating reversed the natural trend.

Scientists still aren’t sure what specifically caused this little ice age, but according to oyster shells, it may have had something to do with a sudden weakening in subarctic ocean current patterns in the North Atlantic.

Researchers believe that temperatures in the North Atlantic have reached a point where sea ice is increasingly melting in the Arctic Ocean, diluting seawater with fresh water and weakening ocean currents.

This, in turn, reduced the amount of heat that currents carried toward the pole, “ultimately enhancing sea ice expansion through positive feedback,” the authors wrote.

The stage is set to return to the age of snow and ice.

Today, we’re going in the opposite direction, but as other recent research suggests, the North Atlantic may be approaching another worrying tipping point.

“If the rapid loss of Arctic sea ice, acceleration of Greenland ice sheet melting, and the associated export of fresh water to major convective regions of the North Atlantic continue, a subarctic cyclic tipping point could again lead to rapid and prolonged regional climate change longevity,” the authors caution.

Clam shells are only a proxy for the climate of the past in the marine environment, but they are quite reliable.

Those used in the current study, oyster quahoge (arctic island), are some of the tallest living organisms on the planet. In 2013, a deep-sea cohoj oyster was found that lived to its 507th year, making it the oldest animal ever found.

Because oysters pull oxygen and carbon isotopes from the water to lay down their calcite shells, the chemical composition of their growth lines can code for annual fluctuations in the marine environment, such as seawater temperature, salinity content and dissolved carbon.

Relying on these actions, the researchers have now found a consistent pattern in long-lived deep-sea oysters that indicates a weakening of sub-polar currents in the North Atlantic on two occasions.

The first episode of weakness occurred between 1180 and 1260 AD, and the second between 1330 and 1380 AD, shortly after some volcanic eruptions (although its role in this turbulent transition is still debated).

In the period between these bouts, shell growth and carbon isotopes in oysters indicate that the ecosystem is keeping pace with environmental changes. But during the second episode, the authors note a decrease in crust growth starting around 1300 CE.

This suggests that the presence of increased sea ice in the area may have disrupted primary production and food supply to the sea floor below, depriving oysters of nutrients. After that, the ecosystem never really returned to baseline.

Her resilience seems to have taken a turn for the worse.

The evidence presented here for sub-Arctic elasticity loss from the Atlantic before 1260, together with evidence for weakening of the potentially bipolar sub-polar circulation, suggests that the onset of [Little Ice Age] It may have occurred in response to the subpolar circulation system passing a tipping point,” the authors wrote.

More research is needed to confirm these findings, especially those involving different climate proxies for comparison. Other studies using a variety of data sources, for example, also point to a possible collapse of the North Atlantic Currents around 1300 CE, linking it to the Little Ice Age as well.

If the North Atlantic is as weak as these studies suggest, this region of the world may be in more trouble than we thought.

The study was published in Nature Connections.

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